1. Technical Field
The present invention relates to a method for driving an electrophoresis display device, an electrophoresis display device, and an electronic apparatus.
2. Related Art
A phenomenon (electrophoresis phenomenon) in which electrophoresis particles are moved by coulomb forces has been known, and an electrophoresis display device using the phenomenon has been developed.
The electrophoresis display device is equipped with a pixel electrode provided in each of a plurality of pixels, a common electrode provided to oppose the plurality of pixel electrodes, and an electrophoresis element that is sandwiched by the plurality of pixel electrodes and the common electrode and that contains electrophoresis particles. The electrophoresis display device performs a display drive by moving the electrophoresis particles by an electrical field occurred by a potential difference between the pixel electrodes and the common electrode.
For example, in JP-A-2002-149115, there is a description about “common voltage swing drive method” for performing update of display by switching the potential of each pixel electrode by using two types of potentials having a relationship of high and low and by also switching the potential of the common electrode by the two types of potentials.
Herein, the common voltage swing drive method will be described with reference to FIG. 16 and FIGS. 17A to 17C.
FIG. 16 is a diagram showing an example of a drive timing chart according to a conventional electrophoresis display device. FIGS. 17A to 17C are diagrams showing a behavior of black particles (electrophoresis particles) 1026 and white particles (electrophoresis particles) 1027 when driven in accordance with the timing chart of FIG. 16. Note that in FIGS. 17A to 17C, the black particles 1026 and the white particles 1027 are fully agitated and an image is to be displayed from a display state with gray.
In FIG. 16 and FIGS. 17A to 17C, a plurality of pixels 1040 are separated into a pixel 1040b for displaying black and a pixel 1040w for displaying white for description.
During a display update time tx of FIG. 16, a high potential (first potential; H) is input to a pixel electrode 1035b of the pixel 1040b, and a low potential (second potential; L) is input to a pixel electrode 1035w of the pixel 1040w. 
The display update time tx is about 2 to 2.5 sec as is different depending on the property of the electrophoresis element. In FIG. 16, the display update time tx is set to 2.0 sec.
A rectangular wave whose cycle is 200 to 500 ms is input to a common electrode 1037. In FIG. 16, a rectangular wave whose cycle is 40 ms (2.5 Hz) in which a high potential time of 200 ms and a low potential time of 200 ms are repeated is input during the display update time tx. That is, during the display update time tx, the rectangular wave is input for five cycles.
Note that the “common voltage swing drive method” in the invention refers to a driving method in which a rectangular wave in which the high potential time and low potential time are repeated is applied to the common electrode 1037 for at least not less than one cycle during the display update time tx.
Next, a behavior of the black particles 1026 and the white particles 1027 when driven based on the timing chart of FIG. 16 will be described with reference to FIGS. 17A to 17C.
First, as shown in FIG. 17A, when the high potential (H) is input to the common electrode 1037, a potential difference occurs between the pixel electrode 1035w to which the low potential (L) is input and the common electrode 1037 in the pixel 1040w, and the white particles 1027 move to the side of the common electrode 1037 and the black particles move to the side of the pixel electrode 1035w. 
On the other hand, in the pixel 1040b, no potential difference occurs between the pixel electrode 1035b to which the high potential (H) is input and the common electrode 1037. Accordingly, the black particles 1026 and the white particles 1027 do not move.
Next, as shown in FIG. 17B, when the low potential (L) is input to the common electrode 1037, no potential difference occurs between the pixel electrode 1035w to which the low potential (L) is input and the common electrode 1037, so that the black particles 1026 and the white particles 10127 do not move.
On the other hand, in the pixel 1040b, a potential difference occurs between the pixel electrode 1035b to which the high potential (H) is input and the common electrode 1037, and the black particles 1026 move the side of the common electrode 1037 and the white particles move the side of the pixel electrode 1035b. 
The behavior when the first one cycle of the rectangular wave in FIG. 16 is applied to the common electrode 1037 is schematically shown in FIGS. 17A and 17B. The rectangular wave whose cycle is one rotation of the high potential (H) and the low potential (L) is further input to the common electrode 1037 for four cycles.
FIG. 17C shows a state right after the potential corresponding to five cycles containing the cycle of the aforementioned FIGS. 17A and 17B is applied. That is, FIG. 17C shows a state of each electrophoresis particles when the display update time tx is finished. The white particles 1027 are gathered at the side of the common electrode 1037 of the pixel 1040w and white is displayed, and the black particles 1026 are gathered at the side of the common electrode 1037 of the pixel 1040b and black is displayed.
According to the common voltage swing drive method, the potential applied to the pixel electrode 1035 and the common electrode 1037 can be controlled by two values of the high potential (H) and the low potential (L). Accordingly, the voltage to be applied can be lowered a circuit structure can be simplified. Further, when a TFT (Thin Film Transistor) is used as a switching element of each pixel electrode 1035, there is a merit that the reliability of the TFT can be assured by a low voltage drive.
However, there is a problem described below in this method. There is a case that the potential input to the pixel electrode 1035 the common electrode 1037 is different from a predetermined voltage due to a current leak from a pixel circuit connected to the pixel electrode 1035, a resistance generated when an element substrate equipped with the pixel electrode and the common electrode provided to oppose the element substrate are electrically connected, a resistance owned by the common electrode 37, or the like.
Accordingly, a potential difference occurs in the pixel in which no potential different should fundamentally occur and the electrophoresis particles may be flown back. As a result, there was a problem in that a phenomenon called flicker was generated. The electrophoresis particles are separated from the electrode and the contrast of a display image is temporally deteriorated by the flicker.
The flicker generated in the conventional common voltage swing drive method will be described with reference to FIG. 18. FIG. 18 is a graph showing reflectance measured in chronological order when the pixel 1040w is displayed with white.
In FIG. 18, the horizontal axis shows elapsed time, and driving based on the timing chart of FIG. 16 is performed during the display update time tx that starts from the timing of about two sec, and thereafter, the display retention time th continues. Note that, the timing of about two sec when the display update time tx is started shows a starting pint of the measurement and the display retention time tx shows a data retention time at the measurement, and there is no other intention in each thereof.
The longitudinal axis shows reflectance when the pixel 1040w is displayed with white and observed from the side of the common electrode 1037. Note that the reflectance does not reach 50% when the display update time tx is passed. This is caused by display property of the electrophoresis element. The reflectance of the electrophoresis element to a standard white reflection plate is generally about 50% although different depending on the spec.
In FIG. 18, the area surrounded by the ◯ of the graph at a lower portion shows a timing at which a first cycle of the rectangular wave is applied.
As shown in FIG. 17B, the low potential (L) is applied to the common electrode 1037 and the pixel electrode 1035w in pixel 1040w that displays white at the timing, so that no potential difference occurs and each electrophoresis particles are supposed to remain in the position. However, as shown in the ◯ in the graph, the reflectance is lowered in reality. This is caused by a potential difference due to the aforementioned current leak or the like and shows that flicker is generated by flow back of the electrophoresis particles.
Further, the flicker generates not only in the first cycle, but also in the second cycle shown by the □ although the level of flicker is reduced. Further, the flicker also generates a little in the third to fifth cycles.
The flickers of the levels can be recognized by a person. Accordingly, the user of the electrophoresis display device suffers from a visual stress due to the flicker.